A vehicle seat hinge assembly for use in a two door vehicle, wherein entry into the rear passenger area necessitates "dumping" of the seatback over the seat cushion, typically comprises a pair of hinged members, preferably strong metal plates, pivotally attached to each other by a common pivot pin. One of the hinged members is attached to the seatback portion of the vehicle seat and the other is attached to the seat cushion portion of the vehicle seat. In such hinge assemblies, there is a first stop means, typically a metal post, mounted on one hinged member, that abuts against an abutment member on the other hinged member, so as to thereby define an upright driving position. This upright driving position may or may not be adjustable independently of the "dumping" of the seatback over the seat cushion, depending upon the particular vehicle application and the hinge mechanism therein necessarily employed.
In order to preclude the seatback from unwantedly "dumping" over the seat cushion, such as might occur during rapid braking of a vehicle, a latching mechanism is employed, either a manually operative latching mechanism or an inertial latching mechanism.
Prior art manually operable latching mechanisms and inertial latching mechanisms for use in vehicle seat hinge assemblies are well known. While various embodiments of such prior art manually operable latching mechanisms and inertial latching mechanisms have been used in vehicle seat hinge assemblies with reasonable success, they all have at least one common drawback. This drawback is exemplified in the form of "chuck", which is a term known in the art that refers to the mechanical lost motion due to the clearances between various adjacent parts within a mechanism, in this case the latching mechanism of a vehicle seat hinge assembly. Clearance is defined as the distance between adjacent parts of a mechanism. Clearance is generally necessary in order to fit the various parts of a mechanism together, and to facilitate smooth operation of the mechanism without jamming. Clearances are, however, often larger than desirable or otherwise necessary for smooth operation because of the variation in size from one replication of a mass produced mechanical part, such as a seat hinge assembly, to the next (i.e., because of manufacturing tolerances). Moreover, in an assembly of mass produced mechanical parts, such as a vehicle latching mechanism of a seat hinge assembly, the clearances between adjacent parts can stack, both positively and negatively, which makes overall latching performance of any particular latching mechanism selected from a set of similarly mass-produced latching mechanisms all the more unpredictable.
Chuck is experienced whenever externally applied forces are applied to the parts of a mechanism so as to cause relative movement between the parts of the mechanism. Such external forces include the forwardly directed momentum of the seatback with respect to the seat cushion, which is experienced during sudden deceleration of a vehicle. Chuck is a highly undesirable characteristic in vehicle seat hinges, for both safety and aesthetic reasons. In terms of safety, the inertia of the seatback is transferred to the torso of a person sitting in that seat, which increases the likelihood of injury to that person in a forward crash situation. In terms of aesthetics, a seatback can visually appear loose, or can rattle, either of which suggests poor quality. In fact, the existence of any chuck, from the marketing point of view, is in diametric opposition with modern trends to increased safety, reliability, and quality of vehicle seats.
In vehicle seats employing a manually operable latching mechanism, there is typically present a selectively releasable latching mechanism that is used to latch the seatback member in the normal upright position, thereby substantially precluding pivotal movement of the seatback member with respect to the seat cushion, for reasons of safety during deceleration of a vehicle. The selectively releasable latching mechanism may be, for example, a pivoting arm with a hook portion on the end thereof, which pivoting arm may be mounted on one of the hinged members. In this manner, the selectively releasable latching mechanism interacts with a second stop means, typically a metal post, that is securely attached to the other hinged member. A handle portion of the selectively releasable latching mechanism extends from the seatback portion of the vehicle seat so as to be readily accessible by a user to selectively latch and release the two hinged members in a set orientation with respect to each other by correspondingly engaging and disengaging the second stop means. The hook portion of the selectively releasable latching mechanism engages the second stop member so as to preclude forwardly directed pivotal movement of the seatback with respect to the seat cushion. As is inherent with any prior art manually operable latching mechanism, there is a small clearance between the hook portion of the pivoting arm and the second stop means, when the latching mechanism is in its latching position, which clearance increases over time with wear. This small clearance allows chuck of the seatback with respect to the seat cushion to occur when the seat cushion is under the influence of a forwardly directed external force, or due to inertia of the seatback during sudden deceleration of the vehicle.
In vehicle seat hinges employing an inertial latching mechanism, there is a further factor causing additional chuck of the seatback with respect to the seat cushion, as will now be described. In a typical prior art inertial latching mechanism, the mechanism for precluding forward motion of the seatback with respect to a seat cushion typically comprises an abutment means located on the hinged member that is attached to the seat cushion and an inertially actuatable moveable latch pawl member pivotally mounted on the hinged member that is attached to the seatback. Such a prior art inertial latching mechanism is well exemplified by the LOW-CHUCK INERTIAL LATCHING MECHANISM FOR SEAT ASSEMBLIES disclosed in U.S. Pat. No. 5,100,202 (Hughes), which patent is incorporated herein by reference.
In the Hughes patent, the latch pawl is pivotally mounted about a pivot pin on one hinged member, for movement between a latching position and an unlatching position. In the latching position, the latch pawl is oriented such that a leading edge thereof is opposed to, but spaced away from an abutment means on the other hinged member. In use, when the inertial latching mechanism undergoes sudden deceleration, so as to decrease its speed in a forward direction, the seatback and the hinged member attached thereto begin to pivot forwardly. The latch pawl, which is mounted on that hinged member, also moves forwardly until it contacts the abutment means, which is on the other hinged member. The distance moved by the latch pawl is in the order of 1/4", which corresponds to about 3.degree. to about 5.degree. of radial lost motion (chuck) of the seatback with respect to the seat cushion. In some earlier inertial seat latches, the chuck of the seatback before latching of the device can be as high as 8.degree., for example, in the mechanism disclosed in U.S. Pat. No. 4,318,569 (Bilenchi et al.) issued Mar. 9, 1982.
It can be seen that a latching mechanism that substantially eliminates chuck of the seatback of a vehicle seat with respect to the seat cushion is not generally known in the prior art, although the reduction of such chuck has posed a continuing problem for vehicle seat hinge designers. As indicated above, such a latching mechanism would be highly desirable for both safety and aesthetic reasons.